As shown in FIG. 1, metallurgical processes such as basic oxygen steelmaking often employ large (typically, about 8 inches to about 16 inches in diameter, approximately 65-85 feet long, and up to approximately 10 tons in weight) water-cooled oxygen lances 1 to efficiently remove oxidizable elements from molten metal 8 below slag 7 in a metallurgical converter such as a basic oxygen furnace 6. Typically, in addition to the primary oxygen ports 2 at the tip 3 of the lance 1, the prior art oxygen lance 1 may include a ring 4 of small oxygen ports 5 located on the outside of the lance 1 a distance up the lance 1 from the primary oxygen tip 3. These lances 1 are known as post-combustion lances. The ring 4 of small ports 5 distributes oxygen to the furnace atmosphere to react with gases from the process and is known as a post-combustion (or “PC”) distributor.
Due to heat transfer requirements, and also to protect the PC distributor from the furnace atmosphere and the localized heat generated from the post-combustion reaction, the PC distributor (and often, the piping associated therewith) is made of high thermal conductivity metals such as high purity copper.
Although the post-combustion lance often is used to direct oxygen into a metallurgical converter, various other gases may be directed through the lance, depending on the reactions desired. Any and all reaction gases directed through the lance are generally referred to hereinafter as a “gas” for convenience, it being understood that the gas may be oxygen or any other reactive or non-reactive gas or gases. Typically, the gas is injected through the lance at very high rates. For example, oxygen may be injected into the lance at rates of between 300 cubic meters/min. and 600 cubic meters/min.
As is well known in the art, lances are subjected to bending stresses during their service lives, particularly during loading and unloading operations and during lance deskulling operations when the lance is typically placed horizontally on the service floor. During movement of the lance, whether for installation or deskulling, the lance typically is lifted only at the upper end (i.e., above the distributor) with the tip at the lower end resting on the floor at some point during such movements. Accordingly, the prior art lance typically is subject to deflection (i.e., substantially or at least partially transverse deflection) due to the bending loads to which it is subjected.
The maintenance interval for a lance is normally driven by lance tip life, with the lance body lasting many times the life of the tip. Lances equipped with the PC distributor typically are prone to severe bending (i.e., permanent deflection) and, in some cases, failure at the PC distributor, because of the relatively low yield strength of the high thermal conductivity components in the PC distributor. Since the introduction of the mid-lance PC distributor (i.e., at least in the 1980s, and possibly earlier), no effective solutions to the bending and/or failure problems have been implemented. Prior art post-combustion lances typically bend after a relatively short period in service, requiring relatively frequent replacement of the PC distributor.
Previous attempts to address this problem included the development of external removable protective sleeves which are put on new and refurbished PC distributor equipped lances to protect the lances during shipping to the user's facilities. However, the protective sleeves must be removed before the lance is put into service. In practice, sleeves are typically removed prior to completion of the unloading and installation of the lance. As a result, the lance is often bent subsequent to the protective sleeve removal, i.e., during the completion of installation, while in service, or while the lance is loaded back onto the truck for return and repair at the end of its maintenance interval.
Other attempts to address these problems included the use of an internal reinforcing tube disposed within the main gas passageway with apertured support collars that allow gas flow through the collars, wherein the internal reinforcing tube is not part of the PC distributor but extends within the main gas passageway upstream and downstream of the PC distributor.